In high power semiconductor modules, an electrical control path often is required to let the module control when to turn on and when to turn off. As the electrical resistivity and inductivity of this path typically has a strong influence on the switching behaviour of the module, it is recommended that this path shows very good electrical conduction.
For some type of high power modules the control path can be simply realised with the help of an aluminium or copper wire bond. But especially for press pack type modules, this control path is realised with the help of a press contact. Presently those press contacts are mostly made from copper spring like parts. However, copper has no spring capability, therefore the parts need to be relatively small to allow them to deform when they are pressed and thus in case they form the press contact. The absence of spring capability as described above also prevents those parts to exert high force on the contact area. Therefore, since the contact resistance is inversely proportional to the applied force to the press contact, those contacts do not show very low contact resistivity but in contrast thereto, the electrical conductivity may be decreased.
The spring capability can be greatly improved by using an alloy instead of pure copper. However, the addition of some alloying element like beryllium may reduce the electrical conductivity of the material and may further considerably increase the cost of the material.
Standard spring steel will provide good mechanical properties, but those steel as well shows comparably high electrical resistivity.
Known from EP 0 989 611 B1 is a power semiconductor module which is formed from small-area individual chips and in which a short circuit of an individual chip does not lead to total failure of the module. According to this prior art, a layer composed of a suitable material, for example, silver or aluminium, is brought into direct contact with one or both of the main electrodes of the silicon semiconductor. The material of this layer may form an eutectic alloy with silicon. It is further provided that a contact stamp electrically connects the chips.
Document EP 2 827 366 A1 describes a power semiconductor module. Such a power semiconductor module comprises a spring element which has an upper contact area for directly or indirectly connecting the spring element to a load plate and which has a lower contact area for directly or indirectly connecting the spring element to a power semiconductor device, wherein the spring element has a plurality of grooves located along the circumference and restricted with respect to the circumference, wherein the grooves provide a spring deflection of the spring element. Such a spring element may be formed as a one-piece unit and may further be formed of copper or based on copper.
Document US 2012/0211799 A1 describes a power semiconductor module. Such a power semiconductor module comprises an electrically conductive area on the baseplate, which is electrically isolated from the base plate. It is further described that the electrically conductive area may be connected by a contact piston.
The publication “The spring for the 21st century” from Helical Products Company further shows spring elements, which are formed as a flexible helix. Such springs are formed from materials such as stainless steel, aluminum, titanium, alloys or plastics.
Known from EP 1 024 530 A1 is further a power semiconductor module, at which a semiconductor chip is contacted via a contact element with a main contact. The contact element comprises two contact areas between which a bulky spiral spring is provided.
However, the solutions according to the prior art still have potential for improvements.
EP 1 024 530 A1 discloses a spring element for a power semiconductor module, whereby the spring element comprises a first part made from a first material and a second part made from a second material. The first part comprises both a first contact portion having a first contact and a second contact portion having a second contact and the first part comprises an electrically conductive path formed from the first contact portion to the second contact portion. The second part is adapted for exerting a spring force onto the first contact portion and the second contact portion for pressing the first contact to a first contact area of a power semiconductor module and the second contact to a second contact area of a power semiconductor module.
DE 27 25 847 A1 also a spring element for a power semiconductor is disclosed